This invention relates to sources for positive ion particle beams. Such beams are suitable for use for bombardment, compression and heating of a pellet of nuclear fusion fuel to fusion temperature, for injection of particles into magnetic fusion machines such as tokomacs, and other known purposes. A fusion apparatus utilizing positive ion particle beams and sources for such beams are disclosed in copending U.S. application Ser. No. 024,314, filed Mar. 27, 1979 and assigned to the same assignee as the present application. Reference may be made to said application for further information on the utility of positive ion particle beams.
Positive ion sources in general include some form of emitter, extractor grid and accelerator grid to produce the positive particle beam, plus a supply of electrons or other negative particles to make the total charge on the beam substantially electrically neutral. Various problems have been encountered in the sources in the past. A high density often is required at the target and a typical density for some applications is in the range of thousands of amperes per square centimeter. Emitting particle beams of such densities is not practical in a controllable manner. However sources have been proposed with relatively large emitter areas with the particle beams being focused to a smaller target area, and with the beams being pulsed with the pulses compressed in time thereby achieving higher density at the target. When light materials such as deuterium are used as the positive ion source, a relatively high energy pulse is required. A heavy material such as cesium or xenon has been proposed but these heavy ions lose electrons during transit and are difficult to focus as well as to accelerate. However it has been discovered that medium weight particles, such as lithium and sodium, can be utilized without encountering the problems associated with heavier particles while at the same time operating with energy inputs substantially less than that required for deuterium, typically with one-tenth of the energy requirement. Accordingly, it is one of the objects of the present invention to provide a new and improved source utilizing ions of medium weight, preferably alkali metals, for the positive particles in the particle beam.
Another problem encountered with particle beam sources has been that associated with high density currents which are self-limiting in many source configurations. It has been discovered that there is an optimum configuration for grids with respect to the emitter and it is another object of the present invention to provide a new and improved source design utilizing such optimum physical configuration.
Typically a pulse power supply is utilized to drive the source and electrical connections are required between the power supply and the various components of the source. The physical arrangement of these electrical connections often is a problem with high density, high voltage systems and it is an object of the present invention to provide a new and improved electrical circuit utilizing a plurality of series capacitors for achieving electrical interconnections. A further object is to provide a new and improved housing design for positioning and maintaining the physical relationship between the various components despite the high temperatures at which source typically are operated.
Other objects, advantages, features and results will more fully appear in the course of the following description.